Acoustic angular momenta and their applications

Acoustic angular momentum is a physical quantity characterizing the rotation of pressure and local particle velocity fields. The acoustic angular momentum was first observed in vortex waves and was found to have many interesting physics including pseudospin based topological effects, spin-momentum locking, and trapping potential for contactless particle manipulations. In this presentation, we will introduce the categorization of acoustic angular momentum into spin and orbital angular momenta. While airborne sound is a longitudinal wave that was long thought to be spinless, we observed the acoustic spin in some special cases. The spin-momentum locking and spin induced torque for particle manipulation were experimentally demonstrated. In addition, the application of acoustic orbital angular momentum in high-speed communication will be discussed. These novel physical acoustic properties have many more applications ranging from underwater exploration to biomedical engineering.